Measuring capacitor

ABSTRACT

A device for measuring the physical characteristics of textile materials, such as slivers, rovings and yarns, is provided in the form of a capacitor having electrodes comprising a pair of substantially parallel bodies of high frequency ceramic material having plane parallel surfaces and being separated by an air space to permit passage of the textile material therethrough. Each ceramic body is provided with one conductive coating forming the capacitor electrode and a surrounding coating serving as a shield. A terminal extends through said ceramic body from one end thereof into contact with the capacitor electrode.

United States Patent Hoffman Aug. 21, 1973 MEASURING CAPACITOR [75]inventor: Dieter Hotfmann, Uster, Switzerland [73] Assignee: ZellwegerLtd., Uster, Switzerland [22] Filed: Aug. 2, 1971 [21] Appl. No.:168,150

301 Foreign Application Priority om Aug. 4, 1970 Switzerland 11710 [52][1.8. CI 317/246, 317/242, 317/261 [51] Int. Cl H01g 1/06 [58] Field ofSearch 3l7/26l, 246, 249 D,

[56] References Cited UNITED STATES PATENTS 2,998,559 8/1961 Smith317/246 I 3,009,10l ll/l96l 3,l70,099 2/1965 3,303,550 2/l967 3,426,2572/l969 Youngquist 317/261 X 3,493,825 2/l970 Khouri 317/261 X 3,5l5,9876/1970 Zurbrick 317/246 X FOREIGN PATENTS OR APPLICATIONS 500,167 2/1939Great Britain 317/261 Primary Examiner-E. A. Goldberg Attorney-Craig,Antonelli & Hill [57] ABSTRACT A device for measuring the physicalcharacteristics of textile materials, such as slivers, rovings andyarns, is provided in the form of a capacitor having electrodescomprising a pair of substantially parallel bodies of high frequencyceramic material having plane parallel surfaces and being separated byan air space to permit passage of the textile material therethrough.Each ceramic body is provided with one conductive coating forming thecapacitor electrode and a surrounding coating serving as a shield. Aterminal extends through said ceramic body from one end thereof intocontact with the capacitor electrode.

6 Claims, 3 Drawing Figures l MEASURING CAPACITOR This invention relatesto a measuring electrode for capacitive measuring.

The capacitive measuring method has proved to be eminently suitable forthe continuous measurement of textile material, especially slivers,rovings and yarns, with regard to their cross-sectional form. Inprinciple, this method employs a plate capacitor with a dielectric whichconsists of air as long as there is no textile material between theplates. In this case, the capacity of this capacitor has a certain basicvalue. If textile material is then introduced into the space between theplates, the capacity changes on account of the relative dielectricconstant of the textile material which differs from one. These changesin capacity can be converted per se into electrical signals by methodsknown for example by connecting the plate capacitor into a highfrequency resonant circuit, in which case the variations in capacityafter the resonant frequency of the resonant circuit.

Providing the quantity of textile material introduced into the platecapacitor is not too large, it is possible to establish a substantiallylinear relationship between the cross section of the textile materialsituated between the plates and the variations in capacity. At the sametime, it is also possible in this way to reduce the influence of themoisture content of the textile material, as part of the dielectric witha dielectric constant different from one, to a level which no longeradversely affects the result of the measurement.

Since the measuring electrodes are actually parts of the plates formingthe capacitor and since the variations in capacity caused by the textilematerial are extremely small, efforts have to be made to ensure thatboth the mechanical and the electrical stability of the measuringelectrodes are extremely high in order to prevent apparent changes inthe measurements obtained through variations in capacity that are notattributable to the quantity of textile material present in thecapacitor. 7

Measuring capacitors of known type assembled into plate capacitorsconsist of metallic electrodes in the form of prismatic rods which aresecured at the requisite intervals to a high-quality insulating plate.In order to avoid additional variations in capacity caused by outsideinfluences upon the stray fields of the capacitors, the electrodes witha high-frequency voltage applied to them have been provided ,withsuitable grounded screens. The arrangement as a whole required extremelycareful assembly and the requisite stability of the basic capacity couldonly be approximated. I I

An object of the present invention is to provide significantimprovements in this respect. Accordingly, the invention provides ameasuring electrode wherein me tallic electrodes are formed by coatingsapplied by vapor deposition to a body of high frequency ceramic material.reproducing the form of the electrodes, the metal layers beingthickened.

At least two such measuring electrodes can be assembled together to forma plate capacitor.

An electrode pattern is advantageously applied to either side of theceramic body, comprising the actual measuring electrode and a protectiveelectrode which seals the measuring electrode ofi from the outside.

Due to the considerable differences in the fiber content of the textilematerial to be tested, several electrodes can be arranged adjacent oneanother at decreasing intervals so as to form plate capacitors with Vtire measuring range with fewer capacitor electrodes. I

As a result, it is smaller, easier to handle and above all lessexpensive.

In the accompanying drawings:

FIG. 1 is a perspective view of a measuring electrode.

FIG. 2 is a plan view, and

FIG. 3 is a side elevation of a measuring capacitor assembled fromseveral measuring electrodes.

The measuring electrode illustrated comprises a prismic insulating body1 of a high-frequency ceramic material with coatings 2 and 3 applied toboth sides by vapor deposition and galvanically thickened; the coating 2forms a protective or shield electrode and the coating 3 forms theactual capacitor electrode. The electrode is fixed betweenplane-parallel spacer members by means of fasteners 4 and 5. Terminals 6and 7 are connected to the protective electrode 2 and a terminal 8 isconnected to the coating 3 inside the insulating body.

The highfrequency ceramic material used as the constituent material forthe electrode bodies enables them to be ground to absolutely parallellateral surfaces. Since the spacer members Il which determine the plateinterval of the capacitor electrodes can also be made plane-parallelwith extreme precision, it is ensured that the structure of thecapacitor as a whole is extremely stable and gives reproduciblemeasurements.

Another advantage of using a high-frequency ceramic material as theelectrode material with metal coatings applied by vapor deposition isthat the dimensions of the electrodes are determined solely by thetemperautre behavior of the ceramic material. The vapor-deposited metalcoatings participate completely in the dimensional changes which theinsulating body undergoes due to variations in temperature. Accordingly,the electrodes are not subjected to any flexural stresses which couldresult in inadmissible changes in the electrode intervals.

The inevitable variations in the zero capacity of the measuringcapacitor consisting of several electrodes attributable to thevariations in temperature can be almost completely compensated bysuitable bridge circuits because the variations which, basically, aresmall are determined solely by the temperature behavior of thehigh-frequency ceramic material and as a result can be allowed for fromthe outset.

FIG. 2 is a plan view of a measuring capacitor assembled from severalmeasuring electrodes. Measuring electrodes 1, 1', 1", 1" and l0, l0,10', 10'' are secured to a base plate 9 and are held apart at strictlypre-. determined intervals by the plane-parallel spacer members 11. Theelectrodes 1, 1' and 10'', 10" are shown in section.

be guided between the measuring elecrodes of such a measuring capacitorwhich forms a unit for measuring cross section of the textile material.I

I claim:

1. A measuring electrode for use in a plate capacitor capable ofmeasuring the physical characteristics of textile materials, such asslivers, rovings and yarns, comprising 7 a body of high frequencyceramic material having plane-parallel surfaces,

at least one conductive coating applied with uniform thickness by vapordeposition to at least one plane surface of said ceramic body, includingaterminal extending through said ceramic body from one end thereof intocontact with said capacitor electrode, and

an additional conductive coating provided on the plane surface of saidceramic body in surrounding relationship to said one coating to serve asa shield, including second and third terminals connected to saidadditional conductive coating by coatings continued on the surface ofsaid body to one end thereof.

2. A device for measuring the physical characteristics I r 4 comprisinga pair of substantially parallel bodies of highfrequency ceramicmaterial having plane-parallel surfaces and being separated by anunobstructed air space to permit passage of the textile materialtherethrough, and

at leat one conductive coating forming a capacitor electrode appliedwith uniform thickness by vapor deposition to at least one plane surfaceof each of said ceramic bodies.

3. A device as defined in claim 2 wherein an additional conductivecoating is provided on the plane surface of each ceramic body insurrounding'relationship to said one coating, said one coating servingas the capacitor electrode and said additional coating serving as ashield.

4. A device as defined in claim 3 wherein said plane surfaces of saidceramic bodies are ground so as to be absolutely plane-parallel and saidbodies being disposed is closely spaced-parallel relationship.

5. A measuring electrode as defined in claim 2 including a terminalextending through said ceramic body from one end thereof into contactwith said capacitor electrode.

6. A measuring electrode as defined in claim 5 including second andthird terminals connected to said additional conductive coating bycoatings continued on the surface of said body to one end thereof.

1. A measuring electrode for use in a plate capacitor capable of measuring the physical characteristics of textile materials, such as slivers, rovings and yarns, comprising a body of high frequency ceramic material having plane-parallel surfaces, at least one conductive coating applied with uniform thickness by vapor deposition to at least one plane surface of said ceramic body, including aterminal extending through said ceramic body from one end thereof into contact with said capacitor electrode, and an additional conductive coating provided on the plane surface of said ceramic body in surrounding relationship to said one coating to serve as a shield, including second and third terminals connected to said additional conductive coating by coatings continued on the surface of said body to one end thereof.
 2. A device for measuring the physical characteristics of textile materials, such as slivers, rovings and yarns, comprising a pair of substantially parallel bodies of high-frequency ceramic material having plane-parallel surfaces and being separated by an unobstructed air space to permit passage of the textile material therethrough, and at leat one conductive coating forming a capacitor electrode applied with uniform thickness by vapor deposition to at least one plane surface of each of said ceramic bodies.
 3. A device as defined in claim 2 wherein an additional conductive coating is provided on the plane surface of each ceramic body in surrounding relationship to said one coating, said one coating serving as the capacitor electrode and said additional coating serving as a shield.
 4. A device as defined in claim 3 wherein said plane surfaces of said ceramic bodies are ground so as to be absolutely plane-parallel and said bodies being disposed is closely spaced-parallel relationship.
 5. A measuring electrode as defined in claim 2 including a terminal extending through said ceramic body from one end thereof into contact with said capacitor electrode.
 6. A measuring electrode as defined in claim 5 including second and third terminals connected to said additional conductive coating by coatings continued on the surface of said body to one end thereof. 